The present invention relates to a twisted nematic (TN) type liquid crystal display device, and more particularly to such a device having a larger twist angle.
A well-known twisted nematic type liquid crystal display device has a 90.degree. twisted helical structure of a nematic liquid crystal which has a positive dielectric anisotropy and is sealed between two substrates having transparent electrodes arranged thereon in desired display patterns. Polarizing plates (polarizers) are arranged on outer surfaces of the electrode substrates with polarization axes (or absorption axes) thereof perpendicular or parallel to the major axes of the liquid crystal molecules adjacent to the substrates. As well known, however, the time-multiplexed drive characteristics of the liquid crystal display device of this type including a luminance-voltage characteristic, a viewing-angle dependence and a time-multiplexability are not satisfactory. Therefore, the practically tolerable maximum of the number of time-multiplexing which corresponds to the number of scanning electrodes is 32 or 64. This limitation cannot satisfy demands to improve the image quality of the liquid crystal display device and to increase the number of data to be displayed which corresponds to the number of scanning electrodes.
U.S. Pat. No. 4,653,841 to Kando, et al has proposed a liquid crystal display device which has a 160.degree.-200.degree. twisted helical structure of a nematic liquid crystal added with a chiral (or optical active) material, thereby providing excellent time-multiplexed drive characteristics and hence excellent image quality even if the number of time-multiplexing is more than 32. Further, JP-A No. 60-107020 has proposed a liquid crystal display device having a 180.degree.-360.degree. twisted helical structure. In these devices, a pair of polarizers having the liquid crystal layer sandwiched therebetween are disposed with the polarization or absorption axes thereof which are inclined by predetermined angles with respect to the major axes or optical axis of liquid crystal molecules adjacent to electrode substrates, respectively. Display is based on the effect of birefringence of light due to the anti-coincidence between the axis of the polarizer and the optical axis of liquid crystal molecules. Therefore, there is a problem in display appearance that light emerging from the device is colored. Typically, the background is yellowish green and the selected or excited point is dark blue.